An electric distance measuring method, which measures a distance based on outgoing light toward an object and reflection light of the outgoing light by the object received by a light receiver, is known in surveying with public works, for example. In an electric distance meter which performs such a method, the same objective lens is used in the outgoing optical path to the object and the reflection optical path from the object (for example, refer to Japanese Unexamined Patent Application Publication No. 2004-69611). In such an electric distance meter, in the optical path passing through the objective lens facing the object, the central area including the optical axis is used as the outgoing optical path and the circumferential area thereof is used as the reflection optical path.
However, in the above electric distance meter, the reflection optical path is set in the circumferential area, so that it is necessary for the reflection light via the reflection optical path not to have a light beam in the central portion. A condensing lens (condensing optical member) for receiving reflection light by a light receiver is generally used in an electric distance meter. Accordingly, it is necessary to use a condensing lens having a large diameter (effective diameter) relative to a large-outer diameter reflection light without having a light beam in the central portion, so that it becomes difficult to downsize the electric distance meter.
Moreover, the electric distance meter can be downsized by reducing the distance between the condensing lens and the light receiver. In this case, in order to reduce the distance between the condensing lens and the light receiver, i.e., in order to reduce the focal length of the condensing lens, it is necessary to use a condensing lens having a large NA (numerical aperture stop). However, if a diameter (effective diameter) of a lens is large, it is difficult to set a large NA compared to a small diameter (effective diameter) lens, and it is difficult to reduce the focal length of the condensing lens.
It is, therefore, an object of the present invention to provide a downsized electric distance meter by using a condensing optical member having a small outer diameter (effective diameter) as a condensing optical member in a light receiving optical system of reflection light from an object, and by reducing a focal length of the condensing optical member without reducing a spread angle to a light-receiving optical fiber, so as to reduce a diameter of the light-receiving optical fiber.